The present invention consists of an improved system for the detection of leakages in the cooling system of blast furnace nozzles. This system is structurally better and functions more effectively than those systems presently used for the same purpose.
Blast furnace nozzles direct hot air blasts with temperatures of 1,000.degree. to 1,300.degree. C. into the interior of the furnace. The air blast originates in tuyeres and is directed into ovens, normally numbering three or four. The air is forced by pressure in the tuyeres into an annular compartment from which various collectors depart, the number of which will vary depending on the diameter and capacity of the furnace. These collectors terminate in the nozzles. The mouths of the nozzles are housed in the interior of the furnace and discharge the air blast at a pressure which can vary from about 1.5 Kgr/cm.sup.2 to about 3 Kgr/cm.sup.2 and at a rate of about 8,000 Nm.sup.3 /h to 20,000 Nm.sup.3 /h per nozzle, depending on the existing inner volumes. For a better graphic idea of this configuration, FIGS. 1 and 2 are included in the set of drawings accompanying this specification and illustrate characteristic diagrams of a blast furnace installation and of the air collector which communicates with the nozzle. These figures will be discussed in detail later in the specification.
The hot air insufflated through the nozzle acts as combustion air to ignite the fuel oil, which is injected in the furnace, and the coke which is also situated inside the furnace. This operation entails flame temperatures which can reach 2,100.degree. C.
It can clearly be understood that due to the temperatures involved in the blast furnace operation, the interior of the nozzles, due to the contact of the mouth thereof with the interior of the furnace, can also reach very high temperatures. Thus, a cooling system is necessary in order to prevent the materials which comprise the nozzles from melting. Typical nozzles are of varied designs; however, these design variations do not alter their function. All types have cooling jackets with water circulation, and almost all are made of copper alloy with a high thermal conductibility. FIGS. 3, 4, 5 and 6 illustrate a typical configuration of a nozzle associated with a blast furnace. These figures will also be discussed in detail subsequently.
Prior art generally depicts nozzles with a single cooling circuit to prevent them from melting due to the high temperatures associated with a blast furnace operation. Also it should be noted that the nozzles are subjected to substantial erosion due to their contact with high temperature particles during the blast furnace operation. Moreover, the more modern techniques of blast furnace design and operation demand that the blast air be of a higher temperature and under a greater pressure than heretofore required; therefore, the cooling of the nozzles should be more precise, more effective, and, above all, more delicate, inasmuch as a cooling system failure could result in the nozzle being burnt or perforated thereby causing the introduction of cooling water into the furnace which would involve substantial risks. Accordingly, the nozzle cooling techniques underwent significant changes to meet the greater demands placed on these systems due to these necessary increases in blast air temperature and pressure.
One solution adopted is a present day technique which consists of providing the nozzles with two independent cooling circuits. One circuit, that of the mouth, cools the part of the nozzle closest to the furnace. This circuit provides cooling water with a greater velocity and pressure; and therefore, it is separated from the rest of the nozzle cooling system where the other circuit is housed. This other circuit provides cooling water with a pressure and velocity practically identical to the prior art cooling circuits. Should the mouth of the nozzle become perforated, the cooling water in the one circuit should be isolated from this area thereby preventing the water from entering the furnace while the other circuit should continue functioning to cool the nozzle. Therefore, with this technique it is not necessary to stop the furnace in order to change the nozzle which results in important savings in time and thereby increases the productivity, and curtails operating expenses, since a stoppage of the blast furnace is very expensive. Accordingly, with this technique, the nozzle could be changed and repaired only during programmed shutdowns.
As best shown in FIG. 7, the cooling circuit of the mouth is a closed circuit. This is because of the aforementioned requirement of high water pressure and velocity. However, this closed cooling circuit makes direct and immediate observation of the cooling water in each furnace nozzle impossible. Heretofore with prior art systems, water was discharged freely from each nozzle to a collector, thus, by observing the amount of water discharged to the collector, cooling circuit leaks could be detected. With the present day techniques of a closed circuit system this is impossible. Typically, the water of the closed circuit for this type of nozzle is at a rate of 30-40 m.sup.3 /h/nozzle. Effective operation of this type of closed circuit system is more essential to the proper operation of the furnace than that of older open systems. Also, the risks involved, including explosion, due to the failure of the closed system are greater than the risks involved due to the failure of the open system.
In view of the above, the need to find an effective method for the detection of leakages in these closed circuit systems is critical, and many methods have been devised; the most commonly used system consists of placing a manometer in the circuit of each nozzle with two rapid valves, one in front of the manometer and the nozzle and the other at the back in the water inlet and outlet pipings. Periodically, the valves are closed, isolating the nozzle from the circuit. Once said closing has taken place, the manometer indicates whether there is a leakage of not. However, this inspection by observation is very subjective and rapid since it can only last for a few seconds inasmuch as if the mouth of the nozzle does not contain water it would burn. Even when done quickly, this method is not safe, because if the mouth becomes perforated after the inspection has been made, water will continuously enter the furnace until a new observation takes place. Furthermore, other systems of observation by means of equipment situated in and around the surroundings of a furnace in use is not recommended. Also, often times the indications of manometers are not accurate or precise, thus making their reliability questionable. In short, other more reliable and, especially, more rapid processes should be devised.
In this light, a present day technique uses another method consisting of the detection of H.sub.2 in the throat of the furnace. This method, besides being slow due to the reaction of the furnace itself, cannot indicate which nozzle produces the water leakage. The continuous analysis of H.sub.2 can manifest not only water leakages in the nozzles, but leakages in jackets and slabs, as well as variations in the consumption of fuel oil. These manifestations indicate that this method is one of confirmation not of direct detection. Consequently, the need to find a truly effective method continues. However, certain parameters of those closed circuit systems necessary for their proper operation have been established. Some of the more interesting parameters are the following:
Substantially Zero Deviation. If an average value of the cooling flow rate at the mouth of the nozzle is Q M.sup.3, an instantaneous value of the flow rate should be within .+-.1 m.sup.3 of Q M.sup.3.
Repeatability of the measurement. This condition is much more important than the preciseness of the measurement.
At present no known system complies with the first condition. Therefore, the lowest detectable threshold of the magnitude of leakage which said systems can detect does not satisfy the needs of blast furnace operators. The majority of the systems presently being experimented with in most blast furnaces are experiencing substantial problems. The following systems are some current examples:
Propeller meters. These cause relatively high losses in charges which consequently result in the need for using pumps having a greater pressure, a fact which results in a greater initial cost and a greater operating cost.
Measurement of variations in ultrasound fields or magnetic fields. The contamination of the water (oxides, gas bubbles, etc.) affects the apparatus, thus falsifying the measurement. On the other hand, this very delicate apparatus should be mounted on the pipe itself, and to prevent the rapid deterioration thereof under extreme environmental conditions in the proximity of the furnace, the pipe should be positioned to allow the apparatus to be situated in conditions premises, but this increases the initial installation cost.
Measurement of the differential pressure with a venturi or diaphragm. The existing systems which use this principle do not comply with the aforementioned condition of substantially zero deviation.
The improvements introduced by the present invention for the detection of leakages in the cooling liquid system involve the use of a detector which corresponds to those utilized by the systems which measure the variations in the differential pressure of the liquid. This improved detector system eliminates the disadvantages mentioned with respect to the other presently existing solutions and presents, when compared therewith, the following advantages:
(a) It has a remarkable substantially zero deviation which permits it to detect leakages in the range of 0.2%;
(b) The measurements are completely repetitive due to the peculiar design of the apparatus included in the invention;
(c) The equipment, which should be situated directly in the pipes, is very sound and could, therefore, be installed in the blast furnace without any need of special premises. On the other hand, the electronic equipment incorporated in the invention is directly positioned in the central control panel of the furnace and is, therefore, completely safe and protected, and it is connected to the mechanical equipment by conductor cables which are readily installed and protected;
(d) The measurements obtained with the present invention are not falsified by the minor impurities which the water may contain; and
(e) The assembly is not affected by the pulses of the hydraulic circuit.
This invention which has the aforementioned advantages is a system which, basically, observes variations of an electromagnetic field, produced by a ferrite, integrated into an assembly which incorporates two hoods for detecting the differential pressure between liquids taken from two points within the cooling system. The variations in the field are produced in a high-frequency current feed coil as a function of the variations in said differential pressure. The signal observed in said coil is converted into a modulated signal, preferably of 0-20 mA, which, subsequently, is directed to an indicator where the alarm and recording system is situated. Use is made of a technique normally employed in the inductive-type systems to process the information coming from the high-frequency coil. These conventional recording, alarm, and information processing systems are familiar to those skilled in the art.
To complement the description and for a better understanding of the characteristics of the invention, a set of drawings accompanies this specification and forms an integral part thereof wherein the invention is illustrated. Thus, these drawings aid in describing the preferred embodiment, while in no way serve to limit the scope of the invention.